1. Field of the Invention
The present invention is directed to a printer means for printing the front side and back side of a band-shaped recording medium having a turn-over means with an appertaining delivery means arranged therein.
2. Description of the Related Art
A high economic customer benefit and a broad spectrum of flexibility are expected to a greatly increasing degree from modern electrographic printer systems. The effective utilization of printing materials as well as the flexible design of the print information play a great part therein.
Endlessly processing (fan-fold) electrographic printer systems that print a band-shaped recording medium on one side have prevailed in the marketplace everywhere that a high device availability given high printing volume and a broad spectrum of printing materials are required. These printer systems, however, have the disadvantage that it is not possible to switch between single-sided and double-sided printing. For the user, this leads both to an economically unfavorable situation as well as to a contradiction of the contemporary demands for efficient utilization of raw materials. Many customer-specific applications that necessarily require double-sided printing (brochures, books, etc.) can thus not be satisfied, particularly since electrographic high-performance printers are especially economical when they are operated interruption-free insofar as possible.
For generating multi-color and backside printing with electrographic printer devices working with continuous stock, European Patent Document EP-B1-01 54 695 has disclosed that two continuous stock printers be operated following one another, whereby the paper printed in the first printer is turned over and is subsequently printed on the second side in the second printer.
The outlay is substantial because of the required second printer.
The publication IBM Technical Disclosure Bulletin, Vol. 22, No. 6, November 1979, pages 2465-2466, also discloses an electrophotographic printer means for printing band-shaped recording media with which it is possible to print the recording medium on both sides. To this end, the recording medium is taken from a supply stack, supplied to a transfer printing station, and provided with toner images on one side. After the fixing step the recording medium is turned over with the assistance of a turn-over means composed of deflection rods and is resupplied to the transfer printing station. After the back side of the recording medium is printed with toner images, another fixing ensues in the fixing step station.
This old reference basically describes duplex printing with continuous stock recording media. However, the proposal never lead to a product. Further, the described electrographic printer means is only suitable for the both-sided printing of the recording medium. A change in operating mode is not provided. The turn-over means composed of deflection rods that is employed requires a manual threading of the recording medium; further, the way in which the deflection rods are arranged requires a great deal of installation space.
A printer means for printing the front side and back side of a band-shaped recording medium has also already been disclosed that contains units generating an intermediate carrier with appertaining toner images, a transfer printing station that transfers the toner images onto the recording medium and a fixing station that each respectively have a usable width of at least twice the band width of the recording medium. After the printing of the front side, the recording medium is conducted via a return channel from the fixing station to a turn-over station in which it is turned over and resupplied to the transfer printing station for printing the back side.
When the recording medium is supplied to the turn-over station via a return channel comprising paper transport rollers, this turn-over station being preferably equipped with a fully automatic threading means, there is thereby the problem that the paper web can, dependent on its nature, jam before it reaches the turn-over means. The involved insertion event must then be repeated.
Given a stop in the printing process, the paper transport must stop the paper web side-suited, and it must be in turn started side-suited given a start of printing.
Since a deceleration distance given every paper web stop and an acceleration distance given every paper web start are required, the paper web must be retracted to such an extent in front of the transfer printing station given a stop event that it can be accelerated given a restart and synchronized for the transfer printing.
The paper transport rollers of the return channel support the retraction motion of the paper transport so that this paper pull-back can be implemented while the tension in the paper web is relaxed insofar as possible. An overload of the paper transport perforations or, respectively, too great a widening of the transport perforations, which leads to positioning errors in the print format after the restart, would be the result without this pull-back relief. The traction roller forces for the print operation must be designed such that it is guaranteed that the paper web is reliably transported out of the fixing station. Further, the traction roller forces dare not be so high that they take effect through the fixing gap between the pressure and fixing rollers and thus disadvantageously influence the paper running in the fixing station. In the back transport step after a paper stop, the traction rollers of the back side web pull the paper load-free from the stacker unit or from an after-processing loop. However, the traction rollers of the front side web must pull the paper web back through the duplex return and the paper web turn-over means. As a result thereof, the resistance is so high that this can lead to paper tearing during the paper pull-back step.